The present invention relates generally to a method, and to the pin and socket interconnection components required, for mounting and electrically connecting a module to a surface mount technology circuit board.
Pin and socket interconnection technology exists in the industry today. The prevalent method in which a pin and socket are attached to a surface mount technology circuit board, to create the attachment in a high capacity production environment, is by press-fitting the pin and socket into their respective circuit boards then reflowing solder paste that was pre-deposited around the interconnection components on the board. However, this requires specialized and expensive through-hole insertion capital equipment to be purchased and placed within the surface mount reflow manufacturing line. The equipment can be as costly as $200,000 per surface mount reflow line. It would also be necessary to run multiple reflow manufacturing lines to handle a normally diverse product line.
In addition, besides incurring significant capital expenditures to incorporate the press-fit pin and socket approach within a factory, this technology is also very limited in its application. The type of circuit board dielectric material and its thickness play an important role in determining if press-fit technology may be utilized. Amplifier designs utilize microwave board materials, which are often fabricated from PTFE materials. This material is Teflon-based and is soft in nature. This softness makes press fitting interconnecting components difficult. Further, the plated-through holes in such materials are less precise than in rigid materials, often resulting in an unreliable connection between the interconnecting component and board. Finally, the board dielectric material often needs to be thin to provide the optimum width transmission lines. These two constraints render the xe2x80x9cpress-fit approachxe2x80x9d unacceptable in many applications, for example, in applications requiring a highly reliable RF connection between amplifier modules and motherboards of power amplifiers used in wireless base stations.
Thus, the present invention is therefore directed to the problem of developing a method of mounting interconnection pin and socket components in printed circuit boards, that method providing the capability of using a standard surface mount reflow manufacturing line, thereby providing a significant amount of flexibility.
It is a further object of the present invention to provide pin and socket interconnection components that may be easily designed into any circuit board and seamlessly incorporated into a standard surface mount reflow manufacturing line. These through-hole interconnection components should be designed and packaged such that they can be assembled to a circuit board with standard surface mount pick and place equipment, which includes the use of standard vacuum nozzles within the pick and place equipment. Finally, the components should allow normal fabrication and assembly variations to be utilized in all aspects of the process.
The present invention solves these and other problems by providing interconnection components including a pin and socket, each having a head diameter that is wide enough such that a standard vacuum nozzle can capture it. The pin tail has two diametersxe2x80x94a smaller diameter for the tail and a slightly larger diameter for the shoulder which is just under the head. The upper or xe2x80x9cshoulderxe2x80x9d portion of the tail, adjacent to the head, is sized so that it assists in centering the pin within the plated through hole of a surface of a circuit board. Similarly, the socket has two diameters below the head: the lowermost smaller xe2x80x9ctailxe2x80x9d diameter, and a larger diameter referred to herein as the xe2x80x9cshoulderxe2x80x9d.
Solder paste, pre-deposited on the circuit board, sits around the periphery of the pin head and the periphery of the socket shoulder upon insertion of the pin and socket into each respective circuit board. When the circuit board is brought up to solder reflow temperatures, the solder flows under the head portion of the pin and the shoulder portion of the socket, and down the plated through hole to provide a mechanical and electrical connection. This reflow process also acts to center the pin/socket within the plated through hole, which aids in reducing tolerances in the pin and socket alignment effort. The diameter of the plated through hole, the diameters of the pin head and pin shoulder, and a precise amount of solder paste, together allow all of the solder to reside in the plated through hole and around the head of the pin.
In one illustrative embodiment of the invention, a pin/surface mount printed circuit board assembly, for providing an electrical connection between a surface mount printed circuit board and a surface mount motherboard, includes a surface mount circuit board having at least one through hole with a diameter and a pin comprising a tail portion, a shoulder portion and a head portion, the tail portion and the shoulder portion having a diameter that is less than the diameter of the at least one through hole, and the head portion having a diameter that is greater than the diameter of the through hole. The diameter of the shoulder portion is such, in relation to the diameter of the through hole, so as to rest inside the through hole and to allow solder to flow under the head portion and down into the through hole, but not as far down as the tail portion, thereby forming a solder joint between the pin and the through hole and assisting in centering the pin in the through hole. An electrical connection between the surface mount printed circuit board and a surface mount motherboard is provided by inserting the tail portion of the pin into a corresponding socket of the surface mount motherboard.
In yet a further embodiment, the solder is provided in a solder mask dam that is supported on the surface mount printed circuit board. And in yet a further embodiment, a preform solder paste is supported on the surface mount printed circuit board.
In a further illustrative embodiment of the invention, a method is provided for mounting an interconnect component into a plated through hole of a printed circuit board, the component having a head portion, shoulder portion and a tail portion, each of the shoulder and tail portions having a diameter that is less than the diameter of the plated through hole and the head portion having a diameter that is greater than the diameter of the plated through hole. The head portion of the interconnect component is captured, the tail portion of the interconnect component is positioned over the plated through hole and is inserted into the through hole and the circuit board is heated to a prespecified solder reflow temperature such that solder around the periphery of the through hole flows under the head portion of the interconnect component and down into the through hole so as to form a solder joint between the pin and the plated through hole. The diameter and length of the shoulder portion, the diameter of the head portion, a diameter of the through hole and a prespecified amount of solder paste, are such so as to prevent the solder from flowing to the tail portion.
In yet a further embodiment of the invention, a separable mechanical and electrical interconnection is provided between a first board and a second board. The interconnection includes a pin having a tail portion sized so as to fit into a plated through hole of the first board, a head portion sized to have a diameter greater than a diameter of the through hole and to rest on top of the plated through hole when inserted therein, and a shoulder portion sized in relation to the plated through hole so as to rest inside the plated through hole and to allow solder to flow under the head portion and down into the plated through hole, but not as far down as the tail portion, thereby assisting in centering the pin in the through hole. The interconnection also includes a socket having a cavity, a tail portion sized so as to fit into a plated through hole of the second board, and a shoulder portion sized in relation to the plated through hole so as to rest on top of the through hole and to allow solder to flow under the shoulder portion and down into the plated through hole, thereby assisting in centering the socket in the through hole. Upon heating, solder, around the periphery of the head portion of the pin and the shoulder portion of the socket, flows under the head of the pin and the shoulder of the socket, thereby forming a soldered electrical connection between the pin and the first board, and between the socket and the second board, respectively. The pin and socket are joined by aligning and inserting the tail portion of the pin into the cavity of the socket, thereby forming a separable mechanical and electrical interconnection between the first board and the second board.
The proposed interconnect components and method provide the capability of quickly and reliably interconnecting thin RF circuit boards with a mounting process that provides structural integrity, allows for modular designs within amplifiers, provides ease of assembly and repair, and provides the necessary float within each individual mated pair such that gang interconnections are possible while withstanding the normal variation seen in standard manufacturing processes.